1. How reliable is a cogeneration plant? On-site generating capacity can increase the reliability and security of both electricity and steam supply. Cogeneration is a proven technology, and has been in extensive use for the last 30 years. Modern gas turbines and reciprocating engines are extremely reliable. Like aircraft engines, they are designed to run without interruption between scheduled maintenance intervals.
Electrical outages can be very expensive for an operating plant. Having a power plant on site eliminates one frequent source of electrical outages-nuisance trips on incoming transmission and distribution lines.
Cogeneration reliability can be further increased with multiple turbines, spares, multiple fuel sources, emergency generators, black start capability, UPS, and other measures if required. Of course, if your utility suffers from insufficient capacity, frequent outages, voltage fluctuations, or brownouts, having your own generation can quickly pay for itself.
2. What if our gas turbine breaks down? Our factory cannot run without electricity and steam. The most economic electrical solution usually involves arranging for standby power from the utility grid. With this scenario the host plant would pay a nominal monthly charge to the utility for having a contracted capacity available, plus pay for any energy actually consumed (in the event that the cogeneration unit was off line). The cogeneration plant generator would be synchronized electrically to the local grid so that power transfer would be seamless in case of a turbine trip.
If a cogeneration plant is replacing an existing steam boiler, the boiler can be retained to provide backup capacity in case of outage. Depending on the boiler configuration, and the steam service required, a burner may be kept on "pilot" or low firing to provide quick response.
3. Can we lease cogeneration equipment or do we have to purchase it? Major components of a cogeneration system can usually be leased. This allows for, in effect, "100% financing." Indeed, with the proper financing scheme, it is possible to use the energy savings from a cogeneration plant to make the lease payments, and thus pay for the equipment. After the lease is paid out, the savings continue. Apex Cogen can arrange for lease financing for both domestic (North American) and international projects, and for new or used equipment.
4. How long will it take to design and install a typical cogeneration plant? For new gas turbines, reciprocating engines, and heat recovery boilers, the manufacturing lead times are approximately 8 to 14 months. This will govern overall project completion, which would then likely be in the order of 14 to 18 months.
The time can be shortened considerably if used equipment is incorporated and if there are no permitting or regulatory issues-in that case, a plant could be running as soon as 8-10 months from financial closing. Where smaller, pre-manufactured or packaged cogeneration equipment is available, it can be installed in a matter of a few months after delivery, depending on tie-ins.
5. What is the expected life of a gas turbine? A waste heat boiler? A "normal" turbine life is usually stated to be 25 years. However, with regular maintenance and overhauls, they can easily be in service for 30-40 years, especially if natural gas is used for fuel. A waste heat boiler ("HRSG") should last for 50 years or so if water quality is maintained.
6. What permits are required to install a cogeneration plant? These vary with the jurisdiction, but usually involve environmental permitting (with NOx emission stipulations), building permits, and interconnection permits for tying into an electrical grid.
7. What sort of fuel can a turbine or recip engine use? Can refinery waste gas streams be used for fuel? How about hydrogen? Both turbines and reciprocating engines can use natural gas or liquid (#2 diesel). Some reciprocating engines can use heavy fuel. Each manufacturer publishes a fuel specification for its equipment that establishes heat content and tolerance for minerals and contaminants. However, a variety of "off spec" fuels can be used in both turbines and reciprocating engines. Some fuels may require modifications to the combustion system, or require more frequent maintenance. Depending on their composition, waste gas streams may be used for turbine fuel, or blended to obtain acceptable criteria. Hydrogen can also be blended with natural gas and used as turbine fuel.
8. What are location based credits (LBC)? A "Location Based Credit" was a credit offered under an Alberta program that was designed to encourage electrical generation in areas near load requirements. The credits were offered to obviate construction of additional transmission line capacity between the province's major generating areas (near coal fields in central Alberta) and its growth areas in the south. Several new generating plants in Alberta were built under this program.
9. What is "due diligence" and why should I have to pay for it? Broadly defined, "due diligence" is a term used to describe a review or examination process. It may be incurred during acquisition or financing of an asset or investment as an assurance to the lender or investor of the value of the project. For assets or projects that generate cash flow, due diligence may describe the process of assessing the underlying value of the cash flows.
A lender or investor may retain an independent consultant to provide due diligence services, and charge the lendee (the project developer, for example) the consultant's fees for making the assessment. Apex Cogen and Apex Energy provide due diligence services for the power and petroleum industries as part of their consulting practices, and may themselves incur costs for due diligence for independent reviews of its financed projects.
The due diligence process depends upon the requirements of the party requesting the services, but usually will involve a fairly detailed review of the assumptions of the financial projections of the project such as income and expense streams, and the technical and engineering aspects such as equipment performance projections. Critical parameters of cogeneration projects such as fuel supply and pricing, gas turbine performance, and electricity sales contracts may receive special attention.
While a borrower or investor may resist paying for the due diligence services, it is sometimes a small price to pay for an expert, critical review of its business plan: changes made to accommodate the recommendations of a due diligence review may ultimately be much less expensive for all concerned than a project that does not meet it financial objectives.
10. How much steam and electricity does a plant have to use to make installation of a cogeneration plant economic? The short answer is around 2-3 MW of electricity and 15-25,000 lb/hour of steam, but smaller plants are economic depending on commodity prices, and certainly have been installed with success. Cogeneration plants up to 3-4 MW and 30,000 lb/hr of steam can be "packaged" on a trailer or skid for easy installation. "Peak shaving" techniques can be used in conjunction with cogeneration plants as well that make smaller installations beneficial.
The critical factor on sizing a cogeneration facility is the host facility's heat (steam, hot water, glycol, oil) load. In general, the more the better. Less of a consideration is the host's electrical load, providing that excess electricity can be sold onto the grid. The waste heat from a 20-25 MW gas turbine will allow production of 70-80,000 lb/hr of steam. More steam can be produced from a duct burning system.
11. What space requirements does a cogeneration plant have? Modern gas turbine-based cogeneration systems are fairly compact, especially the aero-derivative style gas turbines. A 3 MW trailer-mounted cogeneration plant with 30,000 lb/hr boiler, duct burner system and control room can fit on a 10 x 60 ft highway trailer. Reciprocating engines are generally larger, and require a more robust foundation system.
12. Does a cogeneration plant have to be installed in a building, or can it be uncovered? With proper weather protection, cogeneration equipment does not need to be placed inside a building. For colder climates, special considerations may be made for rapid draining of tube-type waste heat boilers in case the turbine is shut down, and enclosures may be used over the gas turbine or engine to reduce noise.
13. How noisy are cogeneration plants? Can their noise be reduced for sensitive areas? Although both combustion turbines and reciprocating engines are noisy, they may come equipped with special noise attenuating panel enclosures. Further noise reduction can be achieved with special buildings and other features. In general, with proper noise control engineering, a cogeneration plant can be installed in very noise sensitive areas such as residential or hospital areas, with little impact.
14. Our plant only runs one shift, 6 days per week. Is that enough to consider cogeneration? It may be, depending upon electricity and fuel prices, and your plant's thermal and electrical load characteristics. In general, 24 hour/365 day operations with fairly constant steam and electrical loads are preferred.
However, each case should be examined individually. It is sometimes possible for instance, to aggregate loads with other nearby plants, or to use steam for a thermal load during the day, and condense the steam in a steam turbine at night to generate additional electricity for sale. These techniques, and others, may convert marginal savings into a project worth pursuing.
15. How often must a gas turbine be serviced and overhauled? How long does this take? Service and overhaul intervals vary with manufacturer, but as a general rule a turbine is usually off line once a year for inspection, and has an overhaul every three years of operation. Inspections may take only 6-8 hours. Overhauls can take 4-6 weeks. Aero-derivative turbines are designed to allow rapid component replacement or swapping of engines, though. This can facilitate short downtimes for overhauls. A leased engine can be brought to site and swapped out in 1-2 shifts. The plant can thus continue to operate with the leased engine while the turbine undergoes overhaul off site. Industrial style turbines are usually overhauled on site, with components sent offsite for refurbishing as required.
16. What quality water is required for a waste heat boiler? In general, demineralized water is required, particularly for applications of steam turbines. A water quality specification should be prepared for each cogeneration application, depending on steam pressure, temperature, and quality. If the water quality is good and steam pressures low, demineralization may not be required.
